Liquids can be concentrated by boiling off essentially pure steam and recovering the remaining residue. When the steam is to be used in a subsequent part of the system (e.g., as boiler feed), any contaminant or corrosive salts dissolved in water droplets entrained in the steam must be removed. Also, when the liquid contains a dangerous substance or pollutant, entrained droplets must not be allowed to escape with the steam. For example, nuclear generation of electric power produces radioactive liquid wastes. Since the water component is by far the largest volume of such wastes, it is necessary to remove all traces of radioactivity before the water is discharged. One method is to concentrate the radioactive wastes by evaporation of the water and then decontamination of the water vapors by separation of any entrained radioactive liquid droplets. Attempts have been made to separate radioactive water droplets from steam by coalescing of the liquid on separator components. Such separators operate efficiently only when the steam flows within some predetermined narrow velocity range. If the steam velocity strays outside such a range, the separator permits so much radioactive water to escape that whatever receives the steam vapors downstream will be seriously contaminated by radioactivity. The necessity of avoiding such contamination puts serious constraints on the permissible variations in the operating capacity of the system.